1. Field of the Invention
This invention relates to lawn and garden equipment and more particularly to a rear-tine tiller which is convertible to selectively operate in both SRT and CRT modes.
2. Background Information
Several types of garden tillers exist for performing various tilling operations in gardens, flowerbeds, lawns and the like. Examples of these types include rear tine SRT (“standard rotating tine”) tillers, rear tine CRT (“counter rotating tine”) tillers and front tine tillers, also commonly referred to as cultivators. While each of these devices will till the earth, each particular construction is optimized for discrete operating conditions or operations.
One type of tiller is known as a rear tine SRT tiller. This machine typically includes power driven drive wheels, power driven tines and a handle which extends over the tines. Thus, during operation, the tines are located between the drive wheels and the operator. The designation SRT indicates that the tines rotate in the same forward direction as the drive wheels and thus cooperate with the wheels to propel the tiller forwardly. These types of tillers are best suited for tilling previously tilled soil or light sandy soil. SRT tillers are also very well suited for power composting.
Rear tine SRT tillers are not however, without their drawbacks. In particular, these machines are not particularly well suited for tilling hard soil, as the tines tend to skip and till only to a very shallow depth. In addition, they tend to be cumbersome and difficult to maneuver in tight areas, such as around existing plants or other obstacles.
Another type of tiller is known as a rear tine CRT tiller. This machine is structurally similar to the rear tine SRT tiller, with the exception that the tines rotate in the opposite direction, namely, opposite to the direction of rotation of the drive wheels. This construction solves some of the problems associated with the SRT tiller described hereinabove, namely, the tines penetrate to a deep depth even in hard soil or soil which has not been tilled previously. A general disadvantage however, of this approach is that the drive wheels tend to lose traction relative to the deep digging “counter rotating” tines. As a result, the tiller may stop moving forward or may even be pulled rearward against the forward pull of the drive wheels. Consequently, such tillers are generally very large and heavy, commonly in excess of 200 pounds, to provide the wheels with sufficient traction to consistently overcome the rearward pull of the tines. A drawback of such large machines however, is that they can be inefficient and cumbersome to operate for relatively light duty tilling, such as home garden use or other small area tilling. CRT tillers are also not suited for power composting.
A further type of tiller is known as a front tine tiller or cultivator. Such a machine typically includes a pair of non-driven wheels, power driven tines and a handle which extends over the wheels. During operation, the wheels are located between the tines and the operator and the tines rotate in the forward direction to propel the tiller forwardly. This type of tiller tends to be highly maneuverable and ideally suited for relatively light duty operations such as tilling small areas or areas between and around plants or other obstacles. The front tine tiller however, is not the best choice for routine tilling operations since the wheels trail the tines and therefore tend to leave tracks or ruts in the freshly tilled earth.
Rather than necessitate owning a separate machine for each of the above described tilling operations, it is desirable to have a single machine capable of operating effectively in more than one mode. For example, it would be convenient to provide a single tiller which is capable of operating in both rear tine SRT and CRT modes for effectively tilling both previously tilled earth, as well as hard packed soil. This may conceivably be accomplished by providing a reversing transmission for selectively changing the direction of rotation of the tines. A significant drawback of this approach however, is that the best performing tines tend to be unidirectional, having a preferred direction of movement through the soil. Generally speaking, such tines have convex leading edges and concave trailing edges. The convex leading edge serves to smoothly cut into and lift the soil while effectively allowing roots and grass to slide off the tine. Using a transmission to simply shift the tines into reverse rotation results in the tines moving through the soil leading with the concave, rather the convex surface. Such backwards movement is undesirable because the concave surface tends to snag and become entangled in roots, grass, and other debris. Accordingly, this approach produces an inefficient CRT tiller.
It is, therefore, desirable to provide a single tilling machine that can be quickly and easily converted by a user to both SRT and CRT tine rotation, while moving the tines through the earth only in their preferred direction of movement.
U.S. Pat. No. 5,896,931 discloses a convertible garden tiller in which the tine shaft is pivotable 180 degrees about a transverse axis, to selectively rotate the tines between an SRT mode and a CRT mode. However, the '931 patent requires the operator to loosen a fastener on the drive shaft and then rotate the tine gearbox 180 degrees in a vertical direction about the horizontal drive shaft axis, then re-tighten the fastener. As the fastener is in close proximity to the sharp tines, this has the danger of severe injury to the operator. Further, the loosened drive shaft is unsupported once the fastener is loosened, and the weight of the tines can cause the gearbox to inadvertently rotate, again presenting danger to the operator. In addition, the fastener interferes with the mechanical integrity of the drive shaft.
There is a need for a convertible tiller that is easily convertible between an SRT mode and a CRT mode without the above disadvantages.